1. Field of the Invention
The present invention relates to an apparatus for controlling a power conversion system for driving an induction motor via a VVVF inverter, and more specifically, relates to a control apparatus of a power conversion system having a DC voltage generating means with a power storage system disposed on the DC power supply side and driving the motor using the power generated by the DC voltage generating means.
2. Description of the Related Art
In so-called inverter railway vehicles in which induction motors are driven via VVVF (variable-voltage variable-frequency) inverter control, all-electric brakes have been put into practical use in which the railway vehicles are stopped by applying only the braking force of electric power and not by using air brakes just before stopping.
It is advantageous to obtain stopping force only via electric power without depending on air brakes, since it not only suppresses abrasion of the brake shoe, which leads to improvement of vehicle maintenance, but also causes no delay of the air brake, which contributes to the enhancement of stopping accuracy.
As described, since there are a number of advantages in stopping the railway vehicle using only electric brakes instead of the conventionally-used air brake, it is possible to obtain great advantages with respect to the abrasion of the brake shoe if it becomes possible to replace the air brake with the electric brake throughout the whole speed region of the railway vehicle.
However, in inverter control, the maximum AC-side output voltage of the induction motor is determined by the DC-side input, that is, the input voltage of the inverter, and since the induction motor of the railway vehicle utilizes the AC output voltage in the high speed region, there is a drawback in that the required brake force cannot be obtained by applying the electric brake only.
Therefore, attempts have been made to increase the brake force by raising the voltage of the induction motor while applying the brake, for example, by inserting an impedance such as a resist or a capacitor. However, such arrangement has drawbacks in that the regenerative energy during braking is consumed fruitlessly and that the voltage has no continuity. For example, Japanese patent application laid-open publication No. 2002-369304 discloses a system that does not waste regenerative energy, but the voltage thereof has no continuity.